Generally, windows operating systems have not supported mounting of nested file system volumes. In such operating systems, each file system volume may operate with no dependencies on other file systems volumes. If a file system performed operations, such as, for example, flushing data, locking a volume, dismounting a volume, or other operations with system wide implications, there was no concern that an operation on one volume would affect operations on other volumes.
Virtual hard disk (VHD), as well as other disk container formats, are emerging technologies that expose an entire virtual disk, which may be encapsulated as one or more files. Like real disks, virtual disks may have partitions, volumes, directories and files.
When a virtual disk, nested within a volume of a real disk, is surfaced to the operating system, a volume included within the virtual disk may be mounted. A dependency exists between the volume of the virtual disk and the volume of the real disk because an operation on the volume of the virtual disk is, in reality, an operation on the volume of the real disk. A number of types of operations may cause file systems on volumes of virtual disks to become corrupted when the types of operations are performed without regard to file system dependencies. Examples of the types of operations may include, but not be limited to:    1. Dismounting a volume of a real disk—A volume of a real disk, which is dismounted before dismounting of all dependent (or nested) volumes may corrupt file systems of the dependent volumes;    2. System shutdown—Shutting down a volume of a real disk before shutting down all of the dependent (or nested) volumes may corrupt file systems of the dependent volumes;    3. Volume snapshot operation (which makes a copy of a volume)—When a volume snapshot operation is performed on a volume of a real disk before flushing data from caches associated with virtual disks having volumes nested within (or dependent upon) the volume of the real disk, the volume snapshot operation may fail after timing out waiting for writes to the nested (or dependent) volumes to complete on the underlying volume of the real disk; and    4. PlugAndPlay (PnP) user interface does not show all volumes (a volume of a real disk and any nested volumes on virtual disks) that are removed when the real disk is removed.